Don't have radar but like John, I once avoided this situation because when I saw the tug I assumed it had a barge under tow. The towline and barge were invisible against the island behind them. The white line of foam at the bow of the barge was the only part visible in the dark. A barge painted black can disappear on a dark sea, doesn't seem to be a visibility issue in this case.
Made my heart go pitter-pat when I thought about what the result of not recognizing the tug could have been.